Refold heat exchanger

ABSTRACT

A heat exchanger is disclosed that includes heat exchange elements made from a sheet having a plurality of hollow fins. In certain embodiments, the finned sheet is refolded and sealed at a first edge and a second edge to form an interior volume having an inlet manifold adjacent to the first edge, an outlet manifold adjacent to the second edge, and an opening that is opposite the refold of the finned sheet. In certain embodiments, a flow divider is located in the interior volume between the inlet manifold and the outlet manifold with interior tips of the hollow fins in contact with the flow divider. A base element is coupled over the opening of the interior volume, the base element comprising an inlet and an outlet positioned in fluid communication with the inlet manifold and the outlet manifold, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/425,840, filed on Dec. 22, 2010, which is incorporated herein by reference.

BACKGROUND

1. Field

The present disclosure generally relates to systems and methods of transferring heat between fluids and, in particular, heat exchangers configured to transfer heat between continuous flows of two fluids.

2. Description of the Related Art

Industrial processes and consumer products often operate by transferring heat between two fluids. An example is a household refrigerator wherein, in a very simplified view, a circulating coolant absorbs heat from a refrigerated space and then rejects the heat to the ambient air. The heat exchange portions of conventional heat transfer systems typically have fins such as shown in FIGS. 1A and 1B attached to the tubing carrying the coolant. These types of heat exchangers can be complex to fabricate and have an operational performance limit determined by the surface area of the interior of the tube and the mean path that heat must travel from the fluid to the air.

Tubing having circumferential corrugations is often used to allow metal piping systems to accommodate misalignment and angular offsets. FIG. 1C depicts a typical flexure tube section, showing the circumferential corrugations. As the corrugations are oriented perpendicular to the flow through the tube, the fluid within the folds of the corrugations may be stagnant or cause significant drag on the fluid flow through this section.

SUMMARY

One of the drawbacks of conventional heat exchangers is that the fluid to be cooled is exposed only to a limited surface area, typically the interior surface of a smooth cylindrical tube. Another drawback is the difficulty in attaching fins to the tube carrying the fluid to be cooled to improve the thermal coupling of the tube to the external air. Fins can be formed separately and then placed around the tube, which may not provide a good thermal bond between the fins and the tube, or the fins can be brazed or otherwise thermally bonded to the tube in a secondary operation. Alternately, the heat exchanger can be formed from a thick tube and the fins machined directly into the tube or formed by helically co-extruding fins over a central flow tube, both of which produce good thermal connection between the tube and the fins, but the high cost of these techniques typically limit their use to aerospace applications where the added performance is worth the incremental cost. In addition, the performance of a finned heat exchanger of the type shown in FIGS. 1A and 1B are limited by the long mean thermal path that heat must travel from the interior wall of the tube through the fins to reach the air or other cooling fluid.

The heat exchange element and heat exchangers disclosed herein overcome the drawbacks of conventional heat exchangers by providing a large surface area in contact with the fluid to be cooled and/or the surface area in contact with the cooling fluid and a short mean distance for heat to travel between two fluids. Heat exchangers comprising the disclosed heat exchange elements may be less expensive to manufacture and may provide superior performance to conventional heat exchangers.

In certain configurations, a heat exchange element is disclosed that includes a folded sheet refolded and sealed at a first edge and a second edge to form an interior volume having an inlet manifold adjacent to the first edge, an outlet manifold adjacent to the second edge, and an opening opposite the refold of the folded sheet. The folded sheet comprises a plurality of hollow fins. The heat exchange element also includes a flow divider disposed in the interior volume between the inlet manifold and the outlet manifold. A plurality of interior tips of the plurality of hollow fins is in contact with the flow divider. The heat exchange element also includes a base element coupled to a perimeter of the opening of the interior volume. The base element comprises an inlet and an outlet positioned in fluid communication with the inlet manifold and the outlet manifold, respectively.

In certain configurations, a refold heat exchanger for transferring heat from a first fluid to a second fluid is disclosed. The heat exchanger comprises a plurality of heat exchange elements. Each heat exchange element includes a folded sheet refolded and sealed at a first edge and a second edge to form an interior volume having an inlet manifold adjacent to the first edge, an outlet manifold adjacent to the second edge, and an opening opposite the refold of the folded sheet. The folded sheet comprises a plurality of hollow fins. Each heat exchange element includes a flow divider disposed in the interior volume between the inlet manifold and the outlet manifold. A plurality of interior tips of the plurality of hollow fins is in contact with the flow divider. Each heat exchange element also includes a base element coupled to a perimeter of the opening of the interior volume. The base element comprises an inlet and an outlet positioned in fluid communication with the inlet manifold and the outlet manifold, respectively. The first edge of a first heat exchange element is not sealed to the first edge of an adjacent second heat exchange element.

In certain configurations, a method of forming a heat exchange element is disclosed. The method includes the steps of folding a sheet of material to form hollow fins across a width of the sheet to form a folded sheet, flattening a first edge and a second edge of the folded sheet to respectively form first and second flat edges, lifting a portion of the first flat edge and a portion of the second flat edge, refolding the folded sheet such that a first portion of the folded sheet is proximate to a second portion of the folded sheet to form a refolded sheet, sealing the first flat edge and the second flat edge of the refolded sheet to form an interior volume comprising an inlet manifold adjacent to the first flat edge, an outlet manifold adjacent to the second flat edge, and an opening opposite the refold of the folded sheet, and coupling a base element comprising an inlet and an outlet over the opening such that the inlet and outlet are in fluid communication with the inlet manifold and outlet manifold, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide further understanding and are incorporated in and constitute a part of this specification, illustrate disclosed configurations and together with the description serve to explain the principles of the disclosed configurations.

FIGS. 1A-1B depict conventional heat exchangers.

FIG. 1C depicts a conventional flexible tubing segment.

FIGS. 1D and 1E depict a conventional corrugated heat exchanger.

FIG. 1F depicts a conventional process for manufacturing a corrugated heat exchanger.

FIG. 2A depicts an exemplary primary surface heat exchanger that comprises a plurality of heat exchange elements according to certain aspects of this disclosure.

FIG. 2B is a view of the underside of the primary surface heat exchanger of FIG. 2A according to certain aspects of this disclosure.

FIGS. 3A-3B depict details of the construction of an exemplary primary surface heat exchange element according to certain aspects of this disclosure.

FIGS. 3C-3G depict an exemplary manufacturing process 80 for a primary surface heat exchange element according to certain aspects of this disclosure.

FIGS. 4A-4E depict another configuration of a primary surface heat exchange element according to certain aspects of this disclosure.

FIGS. 5A-5C depict another configuration of a primary surface heat exchange element according to certain aspects of this disclosure.

FIG. 6 depicts schematically the flow of the two fluids relative to the primary surface heat exchanger of FIG. 2A according to certain aspects of this disclosure.

FIG. 7A depicts two examples of refold heat exchangers formed from primary surface heat exchange elements according to certain aspects of this disclosure.

FIG. 7B-7C illustrate a first configuration of a primary surface heat exchanger wherein the fins are straight according to certain aspects of this disclosure.

FIG. 7D-7E illustrate a second configuration of a primary surface heat exchanger wherein the fins are formed with a wave pattern according to certain aspects of this disclosure.

FIG. 7F depicts the height and base width of a flow path in a conventional corrugated heat exchanger.

FIG. 7G depicts the height and width of a generally rectangular passage within a fin of a primary surface heat exchange element according to certain aspects of this disclosure.

FIG. 8A depicts an exemplary fabrication process for an example plate-fin heat exchange element according to certain aspects of this disclosure.

FIGS. 8B-8C depicts details of the construction of the heat exchange sheet fabricated using the process depicted in FIG. 8A according to certain aspects of this disclosure.

FIG. 9 is a perspective cut-away view of another example configuration of a plate-fin heat exchanger according to certain aspects of this disclosure.

FIGS. 10A-10B depicts additional details of the construction of the plate-fin heat exchanger shown in FIG. 9 according to certain aspects of this disclosure.

FIGS. 11A-11B depicts a heat exchanger comprising primary surface heat exchange elements according to certain aspects of this disclosure.

FIG. 12A depicts an exemplary heat exchanger system comprising a refold heat exchanger according to certain aspects of this disclosure.

FIG. 12B depicts the operation of the heat exchange system of FIG. 12A according to certain aspects of this disclosure.

FIGS. 13A-13C depict the construction of a large heat exchange system comprising heat exchange elements according to certain aspects of this disclosure.

FIG. 14 depicts an exemplary manufacturing process for a primary surface heat exchange element according to certain aspects of this disclosure.

FIG. 15 depicts an exemplary manufacturing process for a plate-fin heat exchange element according to certain aspects of this disclosure.

DETAILED DESCRIPTION

The following description includes examples of heat exchange elements having a finned wall providing improved thermal coupling between fluids on opposite sides of the wall. Walls of these heat exchangers are folded to form a series of hollow fins having a relatively large height-to-width ratio, compared to conventional heat exchangers, and therefore a larger surface than a circular tube having an equivalent cross-sectional area.

One general type of the disclosed heat exchange elements, referred to herein as “primary surface” heat exchange elements, is designed such that the fluids are separated by only the thickness of the wall that is formed into a series of hollow fins. The fluid inside the heat exchange element flows primarily through passages within the hollow fins, thereby providing a very short mean thermal path between the fluids. A primary surface heat exchanger is over 11 times more efficient, on a volume basis, than a conventional shell-and-tube heat exchanger. The manufacturing process for a primary surface heat exchange element is easily modified to form fins having different heights, widths, and separations as well as to produce heat exchange elements having a range of widths in the flow direction, thereby allowing the heat transfer characteristics to be easily tailored to particular applications. The use of size-specific tooling is reduced or eliminated, thereby simplifying the manufacturing process and the change-over process for reconfiguring a production line to produce a different size of heat exchange element.

A second general type of heat exchange element, referred to herein as “plate-fin” heat exchange elements, has a separation wall with finned heat-coupling walls attached and thermally coupled to one or both sides, thereby increasing the surface area exposed to the fluid on that side of the separation wall. As the transfer of heat across the interface from the fluid into the wall is a limiting factor in the efficiency of the heat exchanger, the additional surface area provided by the heat-coupling walls improves the rate of heat transfer. A plate-fin heat exchanger can be over 4 times more efficient, on a volume basis, than a conventional shell-and-tube heat exchanger. Similar to the primary surface heat exchanger, the manufacturing process for a plate-fin heat exchange element is easily modified to provide heat exchange elements over a range of widths, lengths, and fin dimensions to provide a range of performance capabilities.

Heat exchangers built from either type of heat exchange element are modular and extensible, making it a straightforward activity to provide heat exchanges over a wide range of sizes and capabilities, as is shown herein. The improved performance of primary surface or plate-fin heat exchangers allows a given application to use a heat exchanger that may be an order of magnitude smaller than a conventional device.

In the following detailed description, numerous specific details are set forth to provide an understanding of the present disclosure. It will be apparent, however, to one ordinarily skilled in the art that configurations of the present disclosure may be practiced without some of the specific details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the disclosure.

The method and system disclosed herein are presented in terms of counterflow heat exchangers configured to transfer heat from a first fluid to a second fluid. It will be apparent to those of skill in the art that the heat exchange elements disclosed herein may be used in other types of heat exchangers, such as immersion heat exchangers wherein the external fluid is not actively circulated. In addition, the heat exchange elements are presented as being fabricated from sheet metal in a sequential forming process, whereas it will be apparent to those of skill in the art that the disclosed structures can be fabricated from other materials and/or using other techniques, such as extrusion of a plastic material. Nothing in this disclosure should be interpreted, unless specifically stated as such, to limit the application of any method or system disclosed herein to a particular material, form factor, or fabrication process. Other configurations of heat transfer systems are known to those of skill in the art and the application of the components and principles disclosed herein to other systems will be apparent.

FIGS. 1A and 1B depict conventional heat exchangers 10 and 20. FIG. 1A is a cut-away view of a conventional heat exchanger 10 having a central tube 12 with radial fins 14 attached to the outside of the tube 12. The fins 14 can be either individual generally planar fins or one or more spiral fins that are continuous along the tube 12. FIG. 1B depicts a heat exchanger 20 having fins 14 arranged longitudinally along a smooth-wall tube 12 similar to the tube 12 of FIG. 1A.

FIG. 1C depicts a conventional flexible tubing segment 22. The tube 15 has a series of circumferential corrugations 16 formed in the side wall. The circumferential corrugations 16 are provided solely to allow the tube 15 to bend sideways without the tube 15 collapsing or being reduced in cross-sectional area. The circumferential corrugations 16 may induce additional flow resistance as the flow path through the tube 15 is perpendicular to the corrugations 16.

FIGS. 1D and 1E depict a conventional corrugated heat exchanger disclosed in U.S. Patent Application Publication No. 2005/0217836. FIG. 1D shows a core structure 23 formed from a continuous corrugated sheet 24 folded in a “Z” pattern with corrugated cut sheets 25 inserted between each fold. The corrugations of the continuous sheet 24 and the cut sheets 25 are both formed in a 45° zig-zag pattern, i.e. alternating straight sections wherein each straight section is at right angles to both adjacent straight sections. Four formed headers 26 are coupled to the four corners of the core structure 23 as shown in FIG. 1D.

FIG. 1E shows an assembled conventional corrugated heat exchanger wherein the core structure 23 has been coated on the ends and the exposed sides with a sealing compound 27. The pair of headers 26, 26′ on each side are fluidically coupled such that a flow 28 will enter the inlet header 26 at the front of the right side and emerge from the outlet header 26′ on the right side. As the width of the sheets 25 is the same as the width of the continuous sheet 24, there is no internal manifold space at either end. The flow 28 must zig-zag through the corrugations of the cut sheets 25 and cross-oriented corrugations of the continuous sheet 24 to reach the far side of the interior volumes connected to the header 26. While the flow 28 is shown as a single line that turns corners, in reality flow 28 is a diffuse flow that spreads from the header across and downstream then converges to the outlet header 26′. Similarly, a separate flow 29 entering the inlet header 26 at the back of the left will flow in a diffuse pattern through the spaces between the cut sheets 25 and the continuous sheet 24 and then exit from the outlet header 26′ at the front on the left side.

The heat exchanger of FIGS. 1D and 1E may be complex to manufacture as the headers 26, 26′ are either stamped and folded from sheet metal or molded in the final shape but, in either case, are four additional pieces that must be formed, inventoried, handled, and attached to the core structure 23. In addition, application of the sealing compound 27 is a complex task and may be difficult to complete without the formation of leaks. Furthermore, while the flows 28 and 29 are shown as counterflows within the core structure 23, the tortuous path between the inlet header 26 and outlet header 26′ does not make efficient use of the entire enclosed volume and certain portions of the internal volume, for example, the corners, are likely to be dead spaces.

FIG. 1F depicts a conventional process 210 disclosed in U.S. Pat. No. 6,915,675 for manufacturing a corrugated heat exchange material. A sheet 211 of a formable material is fed into a pair of mated corrugating rollers 214, 215 that form corrugations in the sheet 211. These corrugations are limited in shape to the profiles of non-undercut gear teeth. This limits the aspect ratio, i.e. the ratio of the height of the corrugations to the base width of the corrugations. A plunger 216 is positioned to extend when the smooth sections of the sheet 211 are positioned under the plunger 216, thereby forming a joined series of corrugated folded sections 230.

FIG. 2A depicts an exemplary refold heat exchanger 30 that comprises a plurality of primary surface heat exchange elements 32 according to certain aspects of this disclosure. In this configuration, the heat exchange elements 32 are formed from a continuous sheet of folded metal, i.e. a sheet having a series of fins formed by folding a smooth sheet, that has been refolded to form the walls 40 and ends 42 of each of the heat exchange elements 32. The construction of a primary surface heat exchange element 32 is discussed in greater detail with respect to FIGS. 3A-3G.

FIG. 2B is a view of the underside of the refold heat exchanger 30 of FIG. 2A according to certain aspects of this disclosure. A base element comprising panels 34A, 34B, and 34C has been coupled to the openings formed by the refolded folded metal sheet so as to form inlets 36 and an outlets 38 for all of the heat exchange elements 32.

FIGS. 3A-3B depict details of the construction of an exemplary primary surface heat exchange element 32 according to certain aspects of this disclosure. In FIG. 3A, a portion of the walls 40 and the end 42 have been removed to make the interior volume 44 visible and illustrate how a flow divider 46 is positioned within the interior volume 44. It can be seen how the finned sheet of wall 40 continues from the bottom edge of both walls in a 180° bend to form a wall 40 of adjacent heat exchange elements 32 (not shown) so as to collectively form a refold heat exchanger 30 such as shown in FIG. 2A.

FIG. 3B is an enlarged view of the end 42 of heat exchange element 32 illustrating how the fins 45, described in greater detail with respect to FIGS. 3D and 4D, of the two walls 40 are flattened to form flat edges 42A, 42B that are sealed to each other to form an end 42. In certain configurations, the flat edges 42A, 42B are offset from a plane defined by the interior tips of the fins 45 of walls 40. In certain configurations, the flat edges 42A, 42B are welded to each other. In certain configurations, the flat edges 42A, 42B are brazed to each other. In certain configurations, the flat edges 42A, 42B are soldered to each other. In certain configurations, the flat edges 42A, 42B are bonded to each other.

FIGS. 3C-3G depict an exemplary manufacturing process 80 for a primary surface heat exchange element 32 according to certain aspects of this disclosure. FIG. 3C depicts the overall production line 80 starting with rolls 82 of sheet metal or other formable sheet material, for example a thermoformable plastic. In certain embodiments, the sheet material is metal foil having a thickness in the range of 0.003-0.010 inches. The unformed continuous sheet 83A is supplied from roll 82 into a fin folding tool 84 that, in this example, forms the entire width of the sheet 83A into a series of fins thereby producing the folded sheet 83B. In certain embodiments, the folded sheet 83B has 20-45 fins per inch. The folded sheet 83B is passed through a pair of edge formers 86 (only the near former 86 is visible in FIG. 3C and in FIG. 3E) that flatten the ends of the fins 45 to form a flat edge 42C and form/lift the flat edge 42C along the edge of the folded sheet 83B to form a formed folded sheet 83C having an offset flat edge 42C, as seen in FIG. 3F, along each edge.

The formed folded sheet 83C is refolded into a continuous series of double-layer panels. FIG. 3G shows the refolding process with the tooling removed for clarity. Subsequent to the refolding process, the adjacent edges of the double-layer panels are sealed (the sealing tool is not shown in FIG. 3C) to each other, for example by welding, brazing, soldering, adhesive bonding, or other joining technology. In certain embodiments, the free edges of the sheet 83C are pre-welded, i.e. melted to form a bead along the free edge. In certain embodiments, pre-welding is accomplished using a standard welding/heating process, such as an electric arc, tungsten inert gas (TIG) welding, and laser welding. This pre-welding consolidates the flattened portion of the offset flat edge 42C, adding strength and handleability to the sheet 83C. In certain embodiments, additional material, for example a foil strip, is provided along the edge prior to the pre-welding process and is melted into the bead, thereby further adding stiffness to the edge of the sheet 83C. In embodiments where the edges of the refolded double-layer panels are welded to each other, the quality of the welds are improved by pre-welding the edges.

A base element, in this example continuous sheets of metal provided from rolls 90A, 90B, and 90C, is coupled (the coupling tool is not shown in FIG. 3C) to the underside of the sealed double-layer panels to form panels 34A, 34B, and 34C, seen in FIG. 2B, to form the inlets 36 and outlets 38 (not visible in FIG. 3C but also visible in FIG. 2B) and produce a continuous series of the heat exchange elements 32. The connected string of primary surface heat exchange elements are segmented (a process not shown in FIG. 3C) into groups to form refold heat exchangers 30 or other configurations of refold heat exchangers. In another aspect, the production line 80 includes an insertion station (not shown in FIG. 3C) between the forming tools 88 and the addition of the panels 34A, 34B, and 34C to insert flow dividers 46 into the interior space 44 of each double-layer panel.

FIG. 3D is an enlarged view of the region indicated by the dashed-line box 3D in FIG. 3C. In this example, the sheet 83A is folded into fins 45 having rounded tops and bottoms with a primary width 92 and a secondary width 94 and a fin height 96. In certain examples, the tops and bottom of the fins 45 have non-round profiles. The widths 92, 94 may be equal in some cases while in other cases the widths 92, 94 are different. The widths 92, 94 determine the fins per inch (FPI) of the refold heat exchanger 30. In some cases, the height 96 of the fins 45 may vary along the length of sheet 83B and in the heat exchangers 32.

FIG. 3E is an enlarged view of the region indicated by the dashed-line box 3E in FIG. 3C. Sheet 83B having fins formed across the full width of the sheet is fed into the edge-forming tool 86 that flattens, or crushes, the fins along the edge into a flat edge 42C to form sheet 83C.

FIG. 3F is an enlarged view of the region indicated by the dashed-line box 3F in FIG. 3C showing the flat edge 42C and the central fins 45 previously shown in FIGS. 3A and 3B. It can be seen that the flat edge 42C is offset from the bottom of the fins in the central portion of the sheet 83C.

In other aspects of the present disclosure, the flat sheet 83A can be formed into corrugations across only the center section of the sheet (not shown) leaving flat regions 42C along each edge, thereby eliminating the need to reform a flat edge from a finned profile. The ability to form the configuration of sheet 83C having fins in the center and flat edges depends at least in part on the material and the thickness of the sheet 83A.

Alternate manufacturing processes can includes stamping (not shown) of metal or plastic sheets to directly form continuous sheets or discrete panels (not shown) having the fins 45 and flat edges 42C of the formed folded sheet 83C as well as vacuum forming, pressure forming, or hydroforming (all not shown) of the fins 45 and edges 42C. In some cases, the top edges and/or bottom edges of discrete panels may be joined with header and/or footers (not shown) to form heat exchange elements 32. In some cases, side elements (not shown) may be used in place of the flattened portions 42C to join the side edges of the discrete double-layer panels. In some cases, a bulk material, such as a thermoset resin, may be molded, such as by compression molding or injection molding, directly into the shape of finned sheet 83C of an appropriate size to form side walls 40 of a heat exchange element 32.

FIG. 3G is an enlarged view of the region indicated by the dashed-line box 3G in FIG. 3C showing the folding of the formed folded sheet 83C with the folding tool removed to reveal the forming process. It can be seen how the flat edges 42C of a double-layer panel are positioned proximate to each other prior to being bonded to each other, for example by solder, to form the edge 42 of a heat exchange element 32. This continuous series of heat exchange elements 32 can be segmented in groups so as to form refold heat exchangers 30 as are shown in FIG. 7A.

FIGS. 4A-4E depict a configuration of a primary surface heat exchange element 32A according to certain aspects of this disclosure. In this configuration, the flow divider 46 is omitted and the interior tips 56 of fins 45 of the two walls 40A and 40B are touching. FIG. 4A is a cut-away side view of the heat exchange element 32A wherein the interior surface of wall 40A is visible. At each end, the areas 42 that are sealed to the near wall 40B (removed in this view) are shown as hatched areas 42 at the left and right edges of the wall 40A. The adjacent areas 48B and 48C, hatched at an angle opposite to the hatching of the ends 42, are smooth-walled volumes that form an inlet manifold 48B and an outlet manifold 48C. In the middle of the heat exchange element 32A, fins 45 pass from the inlet manifold 48B to the outlet manifold 48C. The edges of bottom panels 34A, 34B, and 34C are visible along the bottom of the wall 40A.

FIG. 4B is a cross-section view of a complete primary surface heat exchange element 32A taken along the section line 4B-4B in FIG. 4A. The walls 40A and 40B are smooth with the full width of the heat exchange element 32A separating the walls 40A, 40B so as to form the inlet manifold 48B. The seam 42D between the flanges 42A and 42B is visible in FIG. 4B as a vertical line on the interior surface of the end 42.

FIG. 4C is a cross-section view of a complete primary surface heat exchange element 32A taken along the section line 4C-4C in FIG. 4A. The fins 45 of walls 40A and 40B can be seen to be touching each other. The shaded areas indicate the interior volume of the heat exchange element 32A that would be wetted by a fluid contained within the interior volume 44. It can also be seen how the finned sheet forming wall 40A folds over in a 180° bend to form a top 43 and then continue as part of wall 40B.

FIG. 4D is an enlarged view of the portion of FIG. 4C enclosed in the dashed-line circle 4D. It can be seen how the series of hollow fins 45 are formed as a series of convex folds 52 that alternate with concave folds 54. The convex and concave folds 52, 54 are alternately connected by sidewalls 58. Each concave fold 54 has a tip 56 on the side facing the interior volume 44. Each fin 45 has an interior passage 44A bounded by the convex fold 52, the two sidewalls 58A and 58B connected to the convex fold 52, and a plane connecting the tips 56A, 56B of the two concave folds 54A, 54B connected to the respective sidewalls 58A, 58B. Returning to FIG. 4C, it can be seen how the only flow paths from the inlet manifold 48B to the outlet manifold 48C are through one of interior passages 44A of the plurality of fins 45 formed by the finned sheets of walls 40A or 40B.

FIG. 4E is a cross-section view of a complete primary surface heat exchange element 32A taken along the section line 4E-4E in FIG. 4A. Ends 42 are visible at the left and right sides. The two-step offset in regions of the inlet and outlet manifold 48B, 48C provide flow space past the narrow section to allow fluid to pass along the outside of fins 45 when two heat exchange elements 32A are positioned adjacent to each other with the fins 45 in contact. It can be seen how interior passages 44A of either wall 40A or 40B are the sole fluid pathways between inlet manifold 48B and outlet manifold 48C.

FIGS. 5A-5C depict another configuration of a primary surface heat exchange element 32B according to certain aspects of this disclosure. FIG. 5A is a cut-away side view of the heat exchange element 32B wherein the flow divider 46 and the interior surface of wall 40A is visible. In this configuration, the fins 45 extend from one end 42 to the other end 42. In this configuration, a flow divider 46 is disposed within the interior volume 44 between the inlet 36 and the outlet 38.

The flow divider 46 functions to force essentially all of the flow of fluid passing from the inlet manifold 48B to the outlet manifold 48C to flow through the passages 44A formed within the hollow fins 45, thereby increasing the amount of time that each element of the fluid is within close proximity to a wall 45 and thereby improving the heat transfer from the fluid to the wall 45. In certain embodiments, the flow divider 46 comprises a solid portion having two parallel planar solid surfaces, as is shown in FIG. 3A. In certain embodiments, the flow divider 46 comprises a foam material. In certain embodiments, the flow divider 46 comprises a coating over a foam core. In certain embodiments, the flow divider 46 comprises a metal formed into a hollow or solid shape. The flow divider may be formed as any structure that blocks the flow of fluid between the inlet manifold 48B and the outlet manifold 48C outside of the interior passages 44A.

FIG. 5B is a cross-section view of a complete primary surface heat exchange element 32B taken along the section line 5B-5B through the inlet manifold in FIG. 5A. It can be seen how the tips 56 of the walls 40A and 40B are separated by a distance equal to the thickness of flow divider 46, shown as a dashed outline 46A in FIG. 5B.

FIG. 5C is a cross-section view of a complete primary surface heat exchange element 32B taken along the section line 5C-5C in FIG. 5A. It can be seen that flow divider 46 fills the interior volume 44 and the tips 56 of fins 45 contact the flow divider 46. As previously discussed with respect to heat exchange element 32A in FIGS. 4A-4E, it can be seen that interior passages 44A of either wall 40A or 40B form the sole fluid path between inlet manifold 48B and outlet manifold 48C.

FIG. 6 depicts schematically the flow of the two fluids 50 and 60 relative to the refold heat exchange element 32 of FIG. 2A according to certain aspects of this disclosure. FIG. 6 is a cut-away side view of heat exchange element 32B wherein flow divider 46 and the interior surface of fins 45 of wall 40A are visible. The fluid 50 is in contact with the outside surfaces of heat exchange element 32 while fluid 60 is provided at the inlet 36 and removed from outlet 38 through external conduit (not shown in FIG. 6). The fluid 50 is flowing from right to left, in the view of FIG. 6, and is in contact with the external surfaces of the fins 45 of both the visible wall 40A and the removed wall 40B. Fluid 60 is introduced through inlet 36 into the inlet manifold 48B which serves to distribute the fluid 60 across the plurality of fins of both walls 40A and 40B. The fluid 60 flows through the interior passages 44A of the plurality of fins 45 and into the outlet manifold 48C. The presence of the open inlet and outlet manifolds 48B, 48C serve to evenly distribute the flow across all of the passages 44A, i.e. without a difference in the pressure drop from the inlet to each of the interior passages 44A, such that the overall performance of the primary surface heat exchange element 32B is improved. The fluid in the outlet manifold exits through outlet 38. In can be seen that this heat exchange element 32 has been implemented as part of a counterflow heat exchanger wherein the direction of flow of the fluid 60 within the heat exchange element 32 is opposite the direction of flow of the fluid 50. In certain configurations, fluid 60 is a coolant rejecting heat to the fluid 50. In certain configurations, fluid 50 is a gas. In certain configurations, fluid 50 is ambient air. In certain configurations, fluid 60 is a liquid.

FIG. 7A depicts two examples 30D and 30E of refold heat exchangers formed from configurations 32D and 32E, respectively, of primary surface heat exchange elements 32 according to certain aspects of this disclosure. The comparison of the two refold heat exchangers 30D and 30E illustrates how the height of the heat exchange elements 32 can be easily changed according to the needs of a particular application. Likewise, the width of the heat exchange elements, the separation of the heat exchange elements, and the heights and widths of the fins 45 can also be easily varied to adapt the design to particular applications. It can be seen that the fins 45 of heat exchangers 30D and 30E are formed with a “wave” pattern along the length of the fins 45. This pattern is advantageous to prevent nesting of the fins 45 of adjacent heat exchange elements 32, as is discussed in greater detail with respect to FIGS. 7B and 7C.

FIG. 7B-7C illustrate a first example configuration of a primary surface heat exchange element 32 wherein the fins 45 are straight, i.e. without the wave pattern seen in FIG. 7A, according to certain aspects of this disclosure. In FIG. 7B, the fins 45 of a first heat exchange element 32 are positioned with the peak of each fin 45 positioned as indicated by the solid lines 65. The fins 45 of a second adjacent heat exchange element 32 are positioned such that the peaks of the fins of the second adjacent heat exchange element 32 are positioned as indicated by the dashed lines 64. If the two sets of fins 45 are pressed against each other, the fins 45 of the two heat exchange elements 32 can become interleaved.

FIG. 7C is a cross-section of the fin arrangement of FIG. 7B taken along the section line 7C-7C. FIG. 7C illustrates how the fins 45 can become nested when the peaks 66, 67 are offset from each other with straight fins 45. This nesting may reduce the efficiency of the heat exchanger 30 and possibly damage the heat exchange elements 32.

FIG. 7D-7E illustrate a second example configuration of a primary surface heat exchange element 32 wherein the fins 45 are formed with a wave pattern as shown in FIG. 7A according to certain aspects of this disclosure. Similarly to the illustration of FIG. 7B, the peaks of each fin 45 of a first heat exchange element 32 are positioned as indicated by the solid lines 67. The peaks of the fins 45 of the adjacent heat exchange element 32 are positioned as indicated by the dashed lines 66. It can be seen that the wave pattern is reversed and therefore the lines 66 and 67 cross repeatedly along the length of the heat exchange element 32. If the two sets of fins 45 are pressed against each other, the fins 45 of the two heat exchange elements 32 cannot become nested.

FIG. 7E is a cross-section of the fin arrangement of FIG. 7D taken along the section line 7E-7E. In FIG. 7E, the location of the fins 45 on the plane of the cross-section 7E-7E are shown in the light shading whereas the portion of the same fins 45 are shown in dark gray further from the plane of the cross-section plane 7E-7E. It can be seen that the dark portions of the fins 45 that are associated with curves 66 overlap the dark portions of the fins 45 associated with curves 67, which is shown in FIG. 7D by the crossing of the lines 66 and 67. The two sets of fins 45 cannot become nested. This reversal of the curves 66, 67 is a result of the continuation of the finned sheet that forms the fins 45 passing over top 43 of the heat exchange element 32 such that the curves on one side of the heat exchange element 32 are reversed from the curves on the other side of the same element 32 and the adjacent elements 32.

FIG. 7F depicts the height H1 and base width W1 of a flow path in a conventional corrugated heat exchanger as seen in FIG. 1D. The triangular corrugations of continuous sheet 24 are perpendicular to the triangular corrugations of cut sheet 25, creating the flow area 17 at each peak of the cut sheet 25. A height H1 and a base width W1 are defined for this flow area 17 as shown in FIG. 7F. As the folds of sheet 24 are approximate right angles, the ratio of H1 to W1 is 0.5.

FIG. 7G depicts the height H2 and width W2 of a generally rectangular passage 44A within a fin 45 of a primary surface heat exchange element 32 according to certain aspects of this disclosure. In certain embodiments, the sides of fin 45 are parallel and form a generally rectangular passage 44A. While the top of fin 45 is rounded and the bottom corners are splayed outward as they connect to the adjacent fins 45, the shape of the passage 44A is still considered to be generally rectangular with a width of W2 and a height of H2. In this example, it can be seen that the ratio of H2 to W2 is greater than 1.0, and may be approximately 4.0 in the example of FIG. 7G. In certain embodiments, the walls of fin 45 may be slightly angled based on resilience of the material of the walls of fin 45 or tooling clearances, it may still be considered generally rectangular if the angles are not too severe. If the walls become significantly angled and cannot be considered to form a generally rectangular passage 44A, then a base width similar to that shown in FIG. 7F is used to evaluate the ratio of the passage 44A.

FIG. 8A depicts an exemplary fabrication process for an example plate-fin heat exchange element 120 according to certain aspects of this disclosure. In this process, a sheet 102 of material, for example aluminum or copper or other metal or metal alloy, is coated on both sides with a brazing material by sprayers 103A and 103B. In certain configurations, the brazing material comprises a flux. In certain configurations, the brazing material is applied as a film without spraying. Additional sheets of material, for example aluminum or copper or other metal or metal alloy, are provided from rolls 101A and 101B and passed through fin-forming tools 104A and 104B, respectively. In this example, the fin-forming tools 104A and 104B fold the sheets from rolls 101A, 101B into fins 45 across the full widths of the folded sheets 105 and 106, respectively. The folded sheets 105, 106 are brought into contact with the two surfaces of sheet 102 and, in this example, passed through a braze oven 110. In the braze oven 110, the brazing material previously applied to sheet 102 melts and bonds the three sheets 102, 105, 106 together. The bonded sheets pass through edge-forming tools 112 that, in this example, form and offset the edges of the center sheet 102 into smooth “S” shapes, thereby finishing the fabrication of the heat exchange sheet 100. Additional details of the heat exchange sheet 100 are discussed with respect to FIG. 8B. The continuous sheet of heat exchange sheet 100 is refolded in operation 114 (the refolding tool is not shown in FIG. 8A0 to form double-layer panels that, when bonded together, form plate-fin heat exchange elements 120 that are discussed in greater detail with respect to FIG. 9.

FIGS. 8B-8C depict details of the construction of the heat exchange sheet 100 fabricated using the process depicted in FIG. 8A according to certain aspects of this disclosure. In this example, the tips of the fins 45 of sheets 105, 106 that are in contact with sheet 102 are at least partially brazed to the sheet 102. FIG. 8B is a perspective view of the near edge of heat exchange sheet 100. It can be seen that the width of the upper folded sheet 105 is less than the width of the center sheet 102 and the portion of the center sheet 102 that extends past the folded sheet 105 is formed into an “S” that, in this configuration, is offset by a distance that is equal to the height of the find formed in the lower folded sheet 106. It can also be seen that the width of the folded sheet 106 is less than the width of the finned sheet 105. In certain embodiments, the folded sheet 106 is centered on sheets 102, 105 such that two equal spaces 108 are formed at each end. In certain embodiments, the folded sheet 106 is disposed between the ends of sheets 102, 105 and offset from the center towards one side such that unequal spaces 108 are formed at each end. The fins 45 of sheets 105, 106 are open at each end.

FIG. 8C is a cross-section end view of the heat exchange sheet 100 at the point along the production line where FIG. 8B is taken from. In this example, the center sheet 102 is formed at each end into the “S” shape and the folded sheets 105 and 106 are centered on sheet 102. Spaces 108A, 108B are provided at each end of the folded sheet 106.

FIG. 9 is a perspective cut-away view of another example configuration of a plate-fin heat exchange element 120 according to certain aspects of this disclosure. In this configuration, the heat exchange sheet 100 is refolded as shown at the end of the process of FIG. 8A such that the tips of the fins 45 of sheet 106 are in contact. It can be seen in FIG. 9 that at least some of the tips of the fins of sheet 106A of a first sidewall 122A of the heat exchange element 100 are in contact with the tips of the fins 45 of sheet 106B of a second sidewall 122B. As the heat exchange sheet 100 is refolded to form the heat exchanger 120, the tips of the fins 45 of sheets 105A also are in contact with the tips of adjacent fins of sheets 105B. In certain configurations, the fins 45 of sheets 105 and/or 106 are formed into the “wave” pattern shown in FIGS. 7A-7C so as to reduce the tendency to nest and thereby maintain the tip-to-tip spacing of sheets 105 and 106 shown in FIG. 9. A base element 124 is bonded to the lower folds of the heat exchange element 100 so as to form the sealed interior volume within a single plate-fin heat exchange element 120. As shown in FIG. 9, multiple parallel heat exchangers 120 can be formed from a continuous heat exchange element 100.

FIGS. 10A-10B depict additional details of the construction of the plate-fin heat exchange element 120 shown in FIG. 9 according to certain aspects of this disclosure. FIG. 10A is a cross-section end view of a plate-fin heat exchange element 120A and portions of adjacent plate-fin heat exchange elements 120B and 120C. The center sheet 102 of FIG. 8B forms a separation wall 132 that cooperates with the base element 124 (not visible in FIG. 10A, shown in FIG. 9) to form an interior volume 126 shown as the darker shaded area in this cross-section view. The folded sheet 106 forms a first heat coupling wall 136 comprising, in this configuration, a series of fins 130 that are similar to the fins 52 of the primary surface heat exchange element 32 shown in FIG. 4D. Similarly, the folded sheet 105 forms a second heat coupling wall 135 comprising, in this example, fins 130. The tips of fins 130 of heat coupling wall 136 are in contact with the tips of fins 130 of the adjacent heat coupling wall 136, and the tips of fins 130 of heat coupling wall 135 of heat exchange element 120A are in contact with the tips of fins 130 of adjacent heat exchange elements 120B and 120C. A first fluid 126A, such as a mixture of propylene glycol and water, fills the volume 126, including both the interior passages of fins 130 and the spaces between fins 130. An external volume 128, i.e. the space outside of the separation wall 102, is filled with a second fluid 128A, such as air, which fills the interior passages of fins 130 of folded sheet 105 as well as the spaces between the fins 130 of sheet 105.

In certain embodiments, the outlet manifold 148C is larger, i.e. longer in the flow direction, than the inlet manifold 148B to accommodate the expansion of the fluid as it gains heat while flowing through the fins 130 of heat coupling wall 136. This provides a pressure drop across the outlet manifold 148C that is approximately equal to the pressure drop across inlet manifold 148B even though the volume of fluid passing through the outlet manifold 148C is larger than the volume of fluid passing through the inlet manifold 148B. Similarly, the outlet 38 may be larger, i.e. longer in the flow direction, than the inlet 36 so as to provide pressure drops that are approximately the same.

In an example where the first fluid 126A in volume 126 is hotter than the second fluid 128A in volume 128, heat is conducted from the first fluid 126A into both the separation wall 132 directly and into the heat coupling wall 136. As the heat coupling wall 136 is thermally conductive, the heat received from the first fluid 126A passes into the separation wall 132. The presence of the heat coupling wall 136 effectively increases the surface area of the separation wall 132 in contact with the first fluid 126A. When heat transfer across the boundary layer of the first fluid 126A that forms on a surface is a limiting factor in heat transfer, the heat coupling wall 136 may improve the overall heat transfer performance of the refold heat exchanger 120. Similarly, the heat coupling wall 135 receives heat from the separation wall 132 and transfers this heat into the second fluid 128A in parallel with the direct transfer of heat from the separation wall 132 to the second fluid 128A. This effectively increases the surface area of the separation wall 132 and reduces the effect of any boundary layer of the second fluid 128A at the surfaces of the heat coupling wall 135 and the separation wall 132.

FIG. 10B is a top cross-section view of the plate-fin heat exchange element 120A along the dashed line 10B-10B in FIG. 10A. In this view, the inlet manifold 148B and outlet manifold 148C formed by the spaces 108 of FIG. 8B in the heat exchange sheet 100 are shown at each end of the heat coupling wall 136 within the separation walls 132. The “S” shaped portions of center wall 102 have been sealed to each other to form flanges 146 that form a portion of the enclosure of volume 126. In the configuration of FIG. 10B, similar to FIG. 6, the first fluid 126A and the second fluid 128A are shown as flowing past and through the heat coupling walls 106 and 105, respectively, in opposite directions such that the plate-fin heat exchange element 120A operates as a counterflow heat exchanger.

FIGS. 11A-11B depicts a heat exchanger 30E comprising primary surface heat exchange elements 32E according to certain aspects of this disclosure. In certain embodiments, the heat exchanger 30E comprises plate-fin heat exchange elements 120. The heat exchanger elements 32E are arranged in a radial pattern about a central opening 31 such that, relating this configuration to the configuration of FIG. 10A-10B, the second fluid 128A passes axially through the heat exchanger 30E, as shown by the arrows 128A, while the first fluid 126A is provided through inlet 36 and received from outlet 38 within the opening 31.

It can be seen in FIG. 11B that each of the heat exchange elements 32E are curved whereas the heat exchange elements 32 and 32A are generally planar. The separation between adjacent heat exchange elements 32E around the inside edge 140 of opening 31 is less than the separation of the same heat exchange elements 32E at the outside edge 142 of the heat exchanger 30E. The curved profile of each heat exchange element 32E increases the length of each heat exchange element 32E compared to a planar profile arranged in a radial pattern. This fills the entire toroidal-shaped area of the axial cross-section and improves the efficiency, i.e. the heat exchange capability per unit volume, of heat exchanger 30E compared to a design using radial planar heat exchange elements 32 (not shown). The heat exchange elements 32E are otherwise substantially the same as the heat exchange element 32 or 32A.

FIG. 12A depicts an exemplary heat exchanger system 150 comprising a refold heat exchanger 30 according to certain aspects of this disclosure. In this configuration, the refold heat exchanger 30 is configured substantially as shown in FIG. 2A, comprising a plurality of primary surface heat exchange elements 32. In certain configurations, the heat exchanger 30 comprises plate-fin heat exchange elements 120. The inlet 36 and outlet 38 (not visible in FIG. 12A) of the heat exchanger 30 are positioned over flow channels in an external manifold 158 such that inlet 160 and outlet 162 of the external manifold 158 are in separate fluid communication with inlet 36 and outlet 38, respectively. A flow enclosure 156 is positioned over the heat exchanger 30 with an inlet 164 and an outlet 166 (not visible in FIG. 12A).

FIG. 12B depicts the operation of the heat exchange system of FIG. 12A according to certain aspects of this disclosure. In this example, with reference to the fluids of FIG. 6, a first fluid 60 is initially cooler than a second fluid 50. The “cool” first fluid 60 is provided at the inlet 160. The “hot” second fluid 50 is provided at the inlet 164 of the flow enclosure 156. In this example, the direction of flow of the first fluid within the heat exchanger 30 is opposite the direction of flow of the second flow past the outside surfaces of the heat exchanger 30. As the second fluid 50 passes through and around the heat exchanger 30, heat is transferred into the material of the heat exchanger 30 and then into the fluid 60. Thus, the first fluid 60 received from the outlet 162 is warmer than fluid 60 entering the inlet 160 and the fluid 50 leaving outlet 166 is cooler than the fluid 50 entering the inlet 164. In certain configurations, the first fluid is warmer than the second fluid and the heat transfer is accomplished in the opposite direction, i.e. from the first fluid 60 to the second fluid 50.

FIGS. 13A-13B depict the construction of a heat exchange system 200 comprising heat exchange elements 30 according to certain aspects of this disclosure. FIG. 13A depicts the assembly of two heat exchangers 30 with an external manifold 158A that is a double-sided version of the external manifold of FIG. 12A to form a heat exchange subassembly 170. The inlet 160 and outlet 162 of the double-sided external manifold 158A are separately and respectively coupled to the inlets 36 and outlets 38 of the individual heat exchangers 32. The heat exchange subassembly 170 is an extensible design, i.e. the heat exchange capacity of the subassembly 170 is a function of the length L and width W and height H of the heat exchangers 30 as well as the number of heat exchangers. In certain implementations, this function is generally linear over a certain range of proportions between L, W, and H. In certain embodiments, the subassembly 170 comprises primary surface heat exchange elements 32. In certain embodiments, the subassembly 170 comprises plate-fin heat exchange elements 120.

FIG. 13B illustrates a higher-level subassembly 180 comprising multiple subassemblies 170 coupled to a center pipe 181. The center pipe 181 is divided internally into flow paths 186 and 188 and comprises a plurality of paired openings 182, 184 along the length of the center pipe 181, wherein the openings 182 are in fluid communication with the flow path 186 and the openings 184 are in fluid communication with flow path 188. In this configuration, when the subassemblies 170 are mated to the center pipe 181, the openings 182 are coupled to the inlets 160 of subassemblies 170 and the openings 184 are coupled to the outlets 162 such that flow path 186 is a common inlet to all of the subassemblies 170 and flow path 188 likewise a common outlet to all of the subassemblies 170 coupled to the center pipe 181.

FIG. 13C illustrates the top-level heat exchanger system 200 comprising a plurality of the subassemblies 180 of FIG. 13B identified as subassemblies 180A-180D. In this configuration, the ends of center pipes 181 of the plurality of subassemblies 180A-180D are coupled in series such that the inlet flow paths 186 are fluidically coupled and the outlet flow paths 188 are likewise fluidically coupled. The ends of flow paths 186 and 188 of the end subassembly 170A respectively form a system inlet 202 and a system outlet 204. A first fluid introduced into the system inlet 202 will flow through the flow paths 186 of all of the subassemblies 180A-180D, then flow into the inlets 160 of each of the subassemblies 170, and then into the inlets 36 of each of the heat exchangers 30. As the first fluid passes through each heat exchanger 30 and out of the outlets 38, the first fluid is collected in the flow channels of external manifolds 158A and passes through the outlets 162 into the flow path 188 of the subassemblies 180 and then out through the system outlet 204. The rear opening of the center pipe 181 of the subassembly 180D can be capped, making the system 200 a stand-alone system, or further connected to another heat exchanger system 200.

FIG. 14 is a flow chart 300 of an exemplary manufacturing process for a primary surface heat exchange element 32 according to certain aspects of this disclosure. The flow chart 300 is related to the process equipment 80 shown in FIG. 3C. In step 305, a sheet of material 83A having a first edge and a second edge is folded to form a series of hollow fins 45, an example fin configuration shown in FIG. 3D, thereby forming a folded sheet 83B. In step 310, the ends of the fins 45 along the first and second edges are flattened to form a flat edge 42C on each side. In step 315, the flat edges are lifted, or offset such that the flat edge 42C is parallel to but offset, as shown in FIG. 3F, from a plane that passes through the interior tips (not visible in FIG. 3F) of the fins 45. In step 320, a portion of the flat edge 42C is pre-welded to consolidate the flattened material and add strength and handleability to the edge 42C. The folded sheet is then refolded in step 325, as shown in FIG. 3G, and the edges are sealed in step 330. If the sealing process comprises welding or brazing, the strength and quality of the seal may be improved by inclusion of the pre-weld process step 315. In step 335, a flow divider 46 is inserted into the interior volume 44 formed by the sealed, refolded sheet. A base element, comprising sheets from rolls 90A, 90B, and 90C in the example of FIG. 3C, is then coupled to the perimeter of the opening of the interior volume 44 in step 340, thereby forming the inlet 36 and outlet 38 and completing the primary surface heat exchange element 32.

FIG. 15 is a flowchart 400 for an exemplary manufacturing process for a plate-fin heat exchange element 120 according to certain aspects of this disclosure. The flow chart 400 is related to the process equipment shown in FIG. 8A. In step 405, sheets of material from one or both of rolls 101A or 101B are folded to form hollow fins thereby forming one or both of folded sheets 105 and 106. The sheets 105 and 106 are bonded on opposite sides of a center sheet that forms the separation wall 102 to form a heat exchange wall 100. The edges of the separation wall 102 are lifted, or offset, in step 415 that to an offset distance that, in the example of FIG. 8A, is equal to the height of the fins of heat coupling wall 106. The heat exchange wall 100 is then refolded in step 420, as shown as item 114 in FIG. 8A, and the edges of the separation wall 102 are sealed in step 425. As base element (not shown in FIG. 8A) that is similar to the base element of FIG. 3C is then coupled to the sealed, refolded heat exchange sheet 100 to form a plate-fin heat exchange element 120.

The concepts disclosed herein provide a system and method of efficiently transferring heat from a first fluid to a second fluid through heat exchangers that comprise fins in contact with one of the fluids. In certain configurations, the fins are in contact with the first fluid on one surface and in contact with the second fluid on a second surface opposite the first surface. In certain configurations, the heat exchangers comprise an internal flow divider configured to cause the internal fluid to flow substantially through interior passages formed by the fins. In certain configurations, the heat exchangers comprise a separation wall with finned heat coupling walls thermally bonded to one or both sides of the separation wall, thereby increasing the thermal coupling between the fluids and the separation wall by increasing the effective contact area between the fluids and the separation wall.

The previous description is provided to enable a person of ordinary skill in the art to practice the various aspects described herein. While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the terms “a set” and “some” refer to one or more. Headings and subheadings, if any, are used for convenience only and do not limit the disclosure.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Some of the steps may be performed simultaneously. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

Terms such as “top,” “bottom,” “front,” “rear” and the like as used in this disclosure should be understood as referring to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference. Thus, a top surface, a bottom surface, a front surface, and a rear surface may extend upwardly, downwardly, diagonally, or horizontally in a gravitational frame of reference.

A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as an “configuration” does not imply that such configuration is essential to the subject technology or that such configuration applies to all configurations of the subject technology. A disclosure relating to an configuration may apply to all configurations, or one or more configurations. A phrase such an configuration may refer to one or more configurations and vice versa.

The word “exemplary” is used herein to mean “serving as an example or illustration.” Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs.

All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim. 

1. A heat exchange element comprising: a folded sheet refolded and sealed at a first edge and a second edge to form an interior volume having an inlet manifold adjacent to the first edge, an outlet manifold adjacent to the second edge, and an opening opposite the refold of the folded sheet, wherein the folded sheet comprises a plurality of hollow fins; a flow divider disposed in the interior volume between the inlet manifold and the outlet manifold, wherein a plurality of interior tips of the plurality of hollow fins is in contact with the flow divider; and a base element coupled to a perimeter of the opening of the interior volume, the base element comprising an inlet and an outlet positioned in fluid communication with the inlet manifold and the outlet manifold, respectively.
 2. The heat exchange element of claim 1, wherein: the plurality of hollow fins are pinched along the first edge and the second edge so as to respectively form a first flat edge and a second flat edge; and the folded sheet is sealed at the first flat edge and the second flat edge to form the interior volume.
 3. The heat exchange element of claim 2, wherein the first and second flat edges are parallel to and offset from a plane through the plurality of interior tips of the plurality of hollow fins.
 4. The heat exchange element of claim 2, wherein the sealing of the first and second flat edges is accomplished by one of the group of welding, brazing, soldering, and crimping.
 5. The heat exchange element of claim 1, wherein: the flow divider is spaced apart from the first and second edges; the space within the interior volume between the flow divider and the first edge forms the inlet manifold; and the space within the interior volume between the flow divider and the second edge forms the outlet manifold.
 6. The heat exchange element of claim 5, wherein: the flow divider comprises first and second surfaces that are substantially planar and parallel to each other; and the interior tips of the plurality of hollow fins are in substantially continuous contact with the flow divider over the length of the flow divider.
 7. The heat exchange element of claim 6, wherein: the plurality of hollow fins and the flow divider form a plurality of isolated passages from the inlet manifold to the outlet manifold; and substantially all of a flow path from the inlet manifold to the outlet manifold is through the plurality of passages of the fins.
 8. The heat exchange element of claim 7, wherein: each passage comprises an internal height and an internal base width; a majority of the plurality of passages have a first height and a first base width; and a ratio of the first height to the first base width is greater than 0.5.
 9. The heat exchange element of claim 8, wherein the ratio of the first height to the first base width is greater than 1.0.
 10. The heat exchange element of claim 9, wherein the ratio of the first height to the first base width is greater than 2.0.
 11. The heat exchange element of claim 9, wherein: the hollow fins each comprise a pair of side walls; the side walls of a majority of the hollow fins are generally parallel to each other, thereby forming a generally rectangular passage having a width; and the ratio of the height of the rectangular passage to the width of the rectangular passage is greater than 2.0.
 12. A refold heat exchanger for transferring heat from a first fluid to a second fluid, the heat exchanger comprising a plurality of heat exchange elements, each heat exchange element comprising: a folded sheet refolded and sealed at a first edge and a second edge to form an interior volume having an inlet manifold adjacent to the first edge, an outlet manifold adjacent to the second edge, and an opening opposite the refold of the folded sheet, wherein the folded sheet comprises a plurality of hollow fins; a flow divider disposed in the interior volume between the inlet manifold and the outlet manifold, wherein a plurality of interior tips of the plurality of hollow fins is in contact with the flow divider; and a base element coupled to a perimeter of the opening of the interior volume, the base element comprising an inlet and an outlet positioned in fluid communication with the inlet manifold and the outlet manifold, respectively, wherein the first edge of a first heat exchange element is not sealed to the first edge of an adjacent second heat exchange element.
 13. The refold heat exchanger of claim 12, wherein: the plurality of hollow fins are pinched along the first edge and the second edge so as to respectively form a first flat edge and a second flat edge; and the first flat edge and the second flat edge are sealed to form the interior volume.
 14. The refold heat exchanger of claim 13, wherein the first and second flat edges are parallel to and offset from a plane through the plurality of interior tips of the plurality of hollow fins.
 15. The refold heat exchanger of claim 13, wherein the sealing of the first and second flat edges is accomplished by one of the group of welding, brazing, soldering, and crimping.
 16. The refold heat exchanger of claim 12, wherein: the flow divider is spaced apart from the first and second edges; the space within the interior volume between the flow divider and the first edge forms the inlet manifold; and the space within the interior volume between the flow divider and the second edge forms the outlet manifold.
 17. The refold heat exchanger of claim 16, wherein: the flow divider comprises first and second surfaces that are substantially planar and parallel to each other; and the interior tips of the plurality of hollow fins are in substantially continuous contact with the flow divider over the length of the flow divider.
 18. The refold heat exchanger of claim 17, wherein: the plurality of hollow fins and the flow divider form a plurality of isolated passages from the inlet manifold to the outlet manifold; and substantially all of a flow path from the inlet manifold to the outlet manifold is through the plurality of passages of the fins.
 19. The refold heat exchanger of claim 18, wherein: each passage comprises an internal height and an internal base width; a majority of the plurality of passages have a first height and a first base width; and a ratio of the first height to the first base width is greater than 0.5.
 20. The refold heat exchanger of claim 19, wherein the ratio of the first height to the first base width is greater than 1.0.
 21. The refold heat exchanger of claim 20, wherein the ratio of the first height to the first base width is greater than 2.0.
 22. The refold heat exchanger of claim 20, wherein: the hollow fins each comprise a pair of side walls; the side walls of a majority of the hollow fins are generally parallel to each other, thereby forming a generally rectangular passage having a width; and the ratio of the height of the rectangular passage to the width of the rectangular passage is greater than 2.0.
 23. A method of forming a heat exchange element, the method comprising the steps of: folding a sheet of material to form hollow fins across a width of the sheet to form a folded sheet; flattening a first edge and a second edge of the folded sheet to respectively form first and second flat edges; lifting a portion of the first flat edge and a portion of the second flat edge; refolding the folded sheet such that a first portion of the folded sheet is proximate to a second portion of the folded sheet to form a refolded sheet; sealing the first flat edge and the second flat edge of the refolded sheet to form an interior volume comprising an inlet manifold adjacent to the first flat edge, an outlet manifold adjacent to the second flat edge, and an opening opposite the refold of the folded sheet; and coupling a base element comprising an inlet and an outlet over the opening such that the inlet and outlet are in fluid communication with the inlet manifold and outlet manifold, respectively.
 24. The method claim 23, wherein the step of sealing is accomplished using a process chosen from the group of welding, brazing, soldering, and crimping.
 25. The method claim 23, wherein the step of coupling is accomplished using a process chosen from the group of welding, soldering, and crimping.
 26. The method claim 23, further comprising the step of: pre-welding the first flat edge and the second flat edge.
 27. The method claim 23, further comprising the step of: inserting a flow divider into the interior volume between inlet manifold and the outlet manifold.
 28. The method claim 23, wherein the step of folding comprises forming hollow fins comprising an internal height, an internal base width, and a ratio of the internal height to the internal base width greater than 0.5.
 29. The method of claim 28, wherein the ratio is greater than 1.0.
 30. The method of claim 28, wherein the step of folding comprises forming generally rectangular hollow fins comprising an internal width and a ratio of the internal height to the internal width greater than 2.0. 